1. Field of the Invention
The present invention relates to a rolling bearing unit with a rotational speed sensor (referred to hereunder as a speed sensing rolling bearing unit), used for rotatably supporting a vehicle wheel on a suspension unit, and detecting the rotational speed of the wheel.
2. Description of the Related Art
There are known speed sensing rolling bearing units such as disclosed in Japanese Patent First Publication KOKAI No. S63-166601, for rotatably supporting a vehicle wheel on a suspension unit, and detecting the rotational speed of the wheel to enable control of an anti-lock braking system (ABS) or a traction control system (TCS).
FIG. 8 shows the speed sensing rolling bearing unit disclosed in the abovementioned publication. An inner ring member comprises a hub 1 and an inner ring 2. A flange 3 for wheel fixture, is provided on an axially outer end portion of the hub 1 (here and throughout the specification, "axially outer end or side" means the outer end or side in a widthwise direction when fitted to a vehicle; the lefthand side in the figures), and an inner ring raceway 4a is formed on an outer peripheral surface at an central portion thereof. The inner ring 2 has an inner ring raceway 4b on an outer peripheral face thereof, and is externally fitted to the outer peripheral surface at the central portion of the hub 1.
A nut 6 is threaded onto a threaded portion 5 formed on an outer peripheral face of the axially inner end portion of the hub 1 (here "axially inner end or side" means the end or side towards the center in a widthwise direction when fitted to a vehicle; the right hand side in the figures). The nut 6 is tightened onto the threaded portion 5 to press against the axially inner end face of the inner ring 2 and thereby secure the inner ring 2 at a predetermined location on the outer peripheral face of the hub 1.
An outer ring member 7 is formed with an outwardly flanged attachment portion 8 for attachment to a suspension unit (not shown), on an outer peripheral face thereof, and a double row outer ring raceway 9a, 9b on an inner peripheral face thereof.
A plurality of rolling bodies 10 are provided between the outer ring raceway 9a, 9b and the inner ring raceways 4a, 4b, so that the hub 1 is rotatably supported inside the outer ring member 7, which is supported on the suspension unit by means of the attachment portion 8.
The rolling bodies 10 are in the form of balls in FIG. 8, but when the bearing unit is for heavy vehicle use, tapered rollers may be used, instead of balls, for the rolling bodies 10.
A ring shaped rotor 11 is provided on the nut 6 and formed with recess/protrusions 12 on the axially inner end face thereof. By means of the recess/protrusions 12, the nut 6 causes a pulsed output to be generated in a sensor 14 (described hereunder) with rotation of the hub 1, and thus functions as a tone wheel.
The sensor 14 is fixed to a cover 13 which is engagingly secured inside an opening at the axially inner end of the outer ring member 7, so that an axially outer end face of the sensor 14 is opposed to the recess/protrusions 12.
With the speed sensing rolling bearing unit as described above, a vehicle wheel fixed to the flange 3 on the axially outer end portion of the hub 1 can be rotatably supported relative to a suspension unit attached to the outer ring member 7. When the rotor 11 formed integrally with the nut 6 which is threaded onto the axially inner end portion of the hub 1, rotates with rotation of the vehicle wheel, the output of the sensor 14 faced to the recess/protrusions 12 on the axially inner end face of the rotor 11 changes.
Since the frequency with which the output of the sensor 14 changes is proportional to the rotational speed of the vehicle wheel, then if the output signal of the sensor 14 is input to a controller (not shown), the rotational speed of the vehicle wheel can be obtained, so that an anti-lock braking system (ABS) or a traction control system (TCS) can be appropriately controlled.
With the conventional speed sensing rolling bearing unit constructed and operated as described above, the cover 13 supports the sensor 14 relative to the outer ring member 7, and the axially outer end portion of the sensor 13 is tightly engaged with the opening at the axially inner end of the outer ring member 7. This is to prevent the cover 13 inadvertently coming off from the outer ring member 7 due to vibrations occurring for example when the vehicle is traveling.
Due to this tight engagement of the outer ring member 7 and the cover 13, separation of the outer ring member 7 and the cover 13 is difficult. Moreover, if the cover 13 is forcefully prized apart from the outer ring member 13 using a tool such as a screwdriver, the cover 13 may be deformed so that it cannot be reused.
Therefore, after the speed sensing rolling bearing unit is installed in the vehicle, for example with use over an extended period, if an abnormality such as a fault occurs in one or other of the rolling bearing portion and the sensor 14, then the whole of the speed sensing rolling bearing unit must be changed including the non faulty part. Not only does this increase the repair cost, but it is also undesirable from the point of view of conservation of resources.
Japanese Utility Model First Publication KOKAI No. H5-14634 discloses a speed sensing rolling bearing unit as shown in FIG. 9 which takes the above into consideration. With this unit, an inner ring member comprises a hub 1 and an inner ring 2. The hub 1 has an outer peripheral face on its axially outer end which is formed with a flange portion 3 for wheel fixture, and a central outer peripheral face which is formed with an inner ring raceway 4a and step portion 15. The inner ring 2 is similarly formed with an inner ring raceway 4b on an outer peripheral face thereof, and is fitted to the outer peripheral face of the hub 1 with its axially outer end face (left end face in FIG. 9) abutted against the step portion 15.
A threaded portion 5 is formed on an outer peripheral face of the hub 1 at its axially inner end portion. A nut 6 is threaded onto the threaded portion 5 and tightened to thereby secure the inner ring 2 at a predetermined location on the outer peripheral face of the hub 1. Recesses/protrusions 16 are formed on the outer peripheral face of the nut 6, so that the nut 6 functions as a tone wheel for detecting rotational speed.
An attachment portion 8 for attaching the outer ring member 7 to a suspension unit (not shown), is provided on the outer peripheral face of the outer ring member 7.
Moreover, outer ring raceways 9a, 9b are formed on an inner peripheral face of the outer ring member 7 so as to be faced to the respective inner ring raceways 4a, 4b.
A plurality of rolling bodies, specifically balls, 10 are provided between the pair of inner ring raceways 4a, 4b and the pair of outer ring raceways 9a, 9b, respectively, so that the hub 1 is rotatably supported inside the outer ring member 7. There is a space for accommodating the plurality of balls 10, which exists between the inner peripheral face of the outer ring member 7 and the outer peripheral faces of the hub 1 and the inner ring 2. Seals 17 is fitted between the inner peripheral face on the axially outer end portion of the outer ring member 7 and the outer peripheral face of the hub 1 and between the inner peripheral face on the axially inner end portion of the outer ring member 7 and the inner ring 2, respectively, to cover the axially inner and outer end openings of the space.
The opening at the axially inner end of the outer ring member 7 (right end in FIG. 9) is covered with a cover 18. The cover 18 is formed in an overall annular shape by press forming a metal plate, and has a base plate 19 formed in a ring shape and a cylindrical wall portion 20 formed by bending an outer peripheral rim portion of the base plate 19 at right angles axially outwards (to the left in FIG. 9). Accordingly, a part of a constant velocity joint can be inserted inside the cover 18. Moreover, a ring shaped step portion 21 is formed on an outer peripheral rim around an axially outer end opening (left end in FIG. 9) of the wall portion 20, which abuts against an axially inner end face 7a of the outer ring member 7.
The outer peripheral rim of the step portion 21 is bent perpendicularly and axially outwards to form an engaging cylindrical portion 22 which is engaged snugly over the axially inner end of the outer ring member 7. Moreover, the opening portion at the axially outer end of the engaging cylindrical portion 22 is bent radially outwards and then folded back through 180 degrees to form an engagement portion 23 with a larger radial thickness. The cover 18 is fixed relative to the outer ring member 7 by externally fitting the engaging cylindrical portion 22 onto the axially inner end portion of the outer ring member 7, with the step portion 21 abutted against the axially inner end face 7a of the outer ring member 7. The engagement strength between the engaging cylindrical portion 22 and the axially inner end of the outer ring member 7 is sufficiently strong to prevent separation of the cover 18 from the outer ring member 7, due for example to vibration accompanying vehicle running.
A sensor 14 such as an electromagnetic type sensor is retained inside the cover 18, and the output from the sensor 14 is sent to a controller (not shown in the figure) by way of a lead 24.
With the rotational speed sensing bearing unit constructed as described above, the operation when rotatably supporting the vehicle wheel relative to the suspension unit, and detecting the rotational speed of the vehicle wheel fixed to the flange 3 of the hub 1, is practically the same as for the speed sensing rolling bearing unit shown in FIG. 8.
With the construction shown in FIG. 9 however, when it is necessary to separate the cover 18 from the outer ring member 7, for example for repair work, then as shown by the chain line in FIG. 9, a tool 25 such as a hand press or a pulley puller is used. The tool 25 has an engaging portion of a split type, and an inner peripheral rim of the engaging portion of the tool 25 is engaged with the end rim of the engagement portion 23 formed on the axially outer peripheral rim around the axially outer end opening of the cover 18. The cover 18 can thus be drawn away from the outer ring member 7 by moving the tool 25 away from the attachment portion 8 in the direction of separation (to the right in FIG. 9), thus removing the cover 18 from the outer ring member 7.
With the conventional construction as shown in FIG. 9, the following points (1) and (2) still remain to be solved.
(1) The height of the engagement portion 23 cannot be sufficiently ensured, and hence engagement between the inner peripheral rim of the tool 25 and the engagement portion 23 is inadequate. PA1 (2) The space between the end rim of the engagement portion 23 which engages with the inner peripheral rim of the tool 25, and the inner end face of the attachment portion 8 on the outer ring member 7 is narrow, so that the thickness of the tool 25 cannot be adequately ensured.
The above first point (1) will now be discussed. Since the engagement portion 23 is formed by bending a portion around the axially outer end opening of the engaging cylindrical portion 22 radially outwards and then folding back through 180 degrees, the radial thickness of the engagement portion 23 is only two times the thickness of the metal plate of the cover 18. Therefore since the plate thickness is around 0.8 mm, then the radial thickness of the engagement portion 23 is only around 1.6 mm. Hence the overlap between the engagement portion 23 and the inner peripheral rim of the tool 25 cannot be sufficiently ensured, with the result that the inner peripheral rim of the tool 25 is easily damaged by crushing during withdrawal, so that the withdrawal operation cannot be reliably carried out.
The above second point (2) will now be discussed. The location of the end rim of the engagement portion 23 to be engaged with the inner peripheral rim of the tool 25, is made to coincide with the location of the opening rim at the axially outer end of the cover 18. Moreover, since the engagement length is made large to ensure adequate engagement strength between the engaging cylindrical portion 22 and the outer ring member 7, it is necessary for the location of the opening rim at the axially outer end to be a reasonable distance from the axially inner end face 7a of the outer ring member 7. As a result, the distance between the opening rim of the engagement portion 23 and the axially inner side face of the attachment portion 8 is reduced, so that the thickness of the engaging portion of the tool 25 must be made small to fit between the opening rim of the engagement portion 23 and the axially inner side face of the attachment portion 8. Accordingly, the configuration of the speed sensing rolling bearing unit may cause problems with ensuring the rigidity of the tool 25, and the cover 18 removal operation is difficult.